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Introduction to Linux - A Hands on Guide

This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own.

I have 3 window server 2003. Each one hosts a VMWare server, which in turn contains both window based and linux based virtual machines.

All the window based virtual machines have no problem connecting to any of the outside world FTP server. But all the linux based (i386-redhat-linux-gnu version 2.4.20-8) virtual machines returns the "421 Service not available, remote server has closed connection" error right after the username is entered. For instance:

ftp> open wirefreethought.com
Connected to wirefreethought.com (66.199.224.58).
220 (vsFTPd 2.0.1)
Name (wirefreethought.com:root): vince
421 Service not available, remote server has closed connection
Login failed.
No control connection for command: Transport endpoint is not connected

The strange things is, if I try "ping hostname" first, then immediately follow by "ftp hostname", everything works fine. Any other time, the above error occurs. Everything worked fine before, until yesterday the problem suddenly occurs.

We've figured out the cause of the problem. We have two different DSL lines. Our router has a capability to intelligently balance accross multiple DSL connections. One of the DSL line has problem with the ftp connection. After we disabled the problematic DLS line, the problem doesn't occur anymore.